For supplying an x-ray tube with energy DC voltage sources with high output voltages are required. For medical applications the acceleration voltage for an x-ray tube is in the range between 15 kV and 160 kV. For industrial applications the acceleration voltage may go up to 400 kV. During the operation the x-ray tube is supplied with power at a few Volts up to 100 kV.
In the prior art power supplies for x-ray tubes having resonance circuit converter topologies are known. Their common principle is to rectify the mains voltage, to smoothen it and to provide it subsequently to a DC/AC converter operating at a high frequency. The DC/AC converter supplies a high voltage transformer with a high frequent AC current. In this way the high voltage transformer forms a high frequent AC current source with a high output voltage. After rectifying and smoothening this voltage, it is provided to the electrodes of the x-ray tube.
The difficulties related to the generation and isolation of high voltages are usually alleviated by dividing the full voltage into two partial voltages having approximately similar maximum values. In general, common potential of the two partial voltages is usually connected to ground. According to this concept for the insulation of a voltage of 150 kV two separate insulation paths against ground are needed. One insulation path insulates +75 kV against ground and the other one −75 kV against ground.
However, for some x-ray application it is desirable to build up the full DC high voltage against ground. In this way it is possible to keep the cathode of the x-ray tube close to ground potential and the anode for example at 120 kV or vice versa. This kind of application calls for a unipolar high voltage supply allowing keeping one electrode of the x-ray tube at the maximum DC voltage whereas the other electrode of the x-ray tube is close to ground potential.
In WO 01/37416 A2 a unipolar power supply with an inverter is disclosed. The power supply has an inverter, which cooperates with a resonance circuit and can be controlled so as to adjust the output power by means of a control unit. The control unit switches the power supply between low and high output power ranges.
In JP 05029091 another type of a high voltage power supply is described. The power supply comprises a plurality of resonant inverter circuits connected in parallel to a DC power supply. A control unit outputs control voltages of variable frequencies to adapt the output power of the high voltage power supply.